1. Field of the Invention
The present invention relates to a coil system and a method for the contact-free magnetic navigation of a magnetic body in a working space.
2. Description of the Prior Art
Coil systems for the contact-free magnetic navigation of a magnetic body employ a plurality of coils to generate a magnetic field which interacts with the magnetic body, as a result of which magnetic forces and torque are generated that bring about the movement of the magnetic body. In this situation, the magnetic force and the magnetic torque which act on the magnetic body can be suitably set by the corresponding currents in the individual coils of the coil system.
In particular, coil systems of the above type are used in the medical field. In this context, a patient is examined by the magnetic body in the working chamber (volume) of the coil system. In this context, the working space is accessible from the outside, and in this space the magnetic forces of the coil system have a sufficient effect on the magnetic body. In order to carry out the examination the magnetic body that is located in the patient and the part of the patient's body that is to be examined are introduced into the working chamber of the coil system. In this situation, the magnetic body constitutes a probe with which measurements can be performed on—in particular images captured of—internal organs of the patient.
A coil system with a magnetic probe is employed for example in gastroenterology, in particular in gastroscopy; see WO 2007/077922 A1. During the endoscopic examination the stomach of the patient is partially filled with water and the patient swallows an appropriate probe that contains a permanent magnet and a camera. The stomach of the patient is located in the working chamber of the coil system, or is introduced into the working chamber after the probe has been swallowed. By using the magnetic forces and torque generated by the coil system, the probe is moved such that captured images of the areas of the patient's stomach lining to be examined are produced. In this situation, it is necessary that a non-homogeneous magnetic field be generated by suitable energization of the coils such that through the interaction of this magnetic field with the permanent magnet in the probe the probe, is suitably positioned and is held in this position.
Different approaches are known for suitably positioning a magnetic body relative to a coil system. A coil system is known from WO 2006/014011 A1, wherein the patient to be examined is moved mechanically with respect to the coil system during the examination. The coil system is constructed such that a single spatial point exists that is fixed with respect to the coil system. If no external forces act on the magnetic body, the body moves toward this spatial point on account of the magnetic forces and torque exerted. When the magnetic body has reached this spatial point, it remains at this spatial point, provided that no forces are exerted from the outside. A disadvantage of this technique is that either the coil system or the patient or both need to be moved mechanically in order to move the magnetic body. This is problematic particularly in the case of applications in which a fast movement of the magnetic body toward a predefined position is required.
Systems are also known in which the coil system is replaced by one or more permanent magnets for moving a magnetic body, see for example U.S. Pat. No. 7,019,610 B2. In these systems also, movement toward a predefined position is achieved by a mechanical movement of the patient, or of the permanent magnet, or of both the patient and the permanent magnet.
Coil systems are furthermore known in which a movement of the magnetic body caused only by the currents in the coil system, without mechanical movement, is achieved by appropriate setting of the magnetic fields and field gradients at the position of the magnetic body (see for example WO 2006/092421 A1). In this situation, however, it is necessary for the position and orientation of the magnetic body to be known, which in turn requires that the position of the magnetic body must additionally be detected.